Engine and Transmission Tech

Progress, I suppose. The old gives way to the new.

I have a new 215, with Piper 270 cam. No chance of getting the SUs re-needled to suit, and anyway I think there is a big vac leak so I'm going to boldly go and fit the JWR/Offenhauser I bought yonks ago, and an Edelbrock 500/1404. There' s a chap with a rolling road in Bristol where I can get it tuned.

Couple of silly questions from someone with nil experience of the 4-barrel:

I want to use the PCV port in the front. It seems to have a plug in it. Can I just drill out the plug?



On the back there's a connector with a small venturi, don't know what that's for, can I just cap it?



Finally, the Rover V8 carb version has no PCV valve, just a flame trap. Should I fit a valve?

Ivor



Edited 1 time(s). Last edit at 08/24/2017 01:51PM by 88v8.

Hello Ivor That port in the back is the pcv port. As far as drilling the front you will have to make sure it is connected to the pcv port, I don't know if you can see that from underneath or not. Good luck with your project.
Bill G

I suspect Bill is right about that Ivor, that rear fitting should be for the PCV. Now how you plumb it though... that depends. There are at least 2 or three ways to skin this cat but there are also several wrong ways and if you do it wrong the usual result is an oily mess. So spend some time making sure you do it right.

The basic configuration falls into one of three camps: American, British, and open.

The American system uses a PCV valve in one rocker cover plumbed to the carb and a large (5/8" or 3/4") vent plumbed to the air cleaner through a flame trap. Usually the carb fitting is unrestricted. At cruise fresh air is drawn in on one side, out the other and into the carb. Under WOT blowby goes out the large tube into the air cleaner.

The British system is difficult to fully understand apparently, hopefully someone who is intimately familiar with it can explain it here. It uses a filtered orifice on one side and a large vent tube and flame trap on the other, plumbed into the intake somehow, but my testing indicates that if that line is exposed to full manifold vacuum the idle becomes uncontrollable due to air leakage past the seals. Wasn't with that carb though, and it could possibly restrict the PCV at idle. You'd need to check. You wouldn't want a restriction in that line at WOT though because then you'll blow oil past all your seals.

The open system simply vents the crankcase to atmosphere.

I would remove that orifice fitting from the carb, plumb your PCV line in there, and route the hose from the Lucas flame trap to the base of the air filter. Many have an installable fitting for that purpose. You may need to tune the carb for the possible increase in air.

Should give you a nice boost over the SUs, please if you would , report back with your impressions.

Jim

I used to have the same carb. On mine the front was also plugged. In the rear I used a fitting for brake servo since I did not have a provision for take off in the manifold.

Here's two photos of my Edelbrock (Weber) 1405 carb (500cfm). There are 3/8" nipples in front and back.

The front port on the carb is designed for use as the PCV port Ivor.
The rear port is intended for use as a vacuum take off for accessories such as power brakes.
The front port is designed in a manner that mixes the incoming vapors with the fuel emulsion from the primary circuit at low throttle angles.
The rear port just dumps directly into the intake plenum potentially allowing oil vapors to condense and pool on the intake floor.
In reality either one works just fine for either purpose.
Your carb looks to be set up for the European style of ventilation. So it might be easiest to use that system.
There is a good write-up somewhere in here on the various PCV systems and their various advantages.
But to answer your question, certainly you can drill out the plug and use the port.

Cheers
Fred



Edited 1 time(s). Last edit at 08/22/2017 09:16PM by DiDueColpi.

General Motors used AFB carbs. on millions of cars. The front port was for the vacuum advance unit on the dist. and the rear was used for the PCV valve. Power brake boosters were plumbed directly into the intake manifold rear runner.

Thankyou.

Funny isn't it, how a seemingly minor issue can become rather difficult.
Before swapping out my old engine I ran it for a day or so venting to atmosphere. Was amazed at the amount of blow that came out !! Well, it would keep the engine bay from rusting.

Here's the factory system. There's a small filter at the rear of the left rocker box, and the flame trap at the front right. No PCV.
All the blowby is sucked in after the dashpot, so it doesn't foul the innards of the carbs..



Anyway, I found the Edelbrock carb installation guide online. It says the rear port is for the servo, and the front for the pcv.

Spoke to Real Steel, they don't sell the fitting for the front port. He seemed rather bemused that I was looking for one. 'It's just a tube' he said.
That rang a bell, so into the attic where I have an AFB 9511, the ancestor of the Edelbrock, and yes there's the connector, it's a pressed-in tube.



Here's the underside. 200cfm primaries, plus I have a dual-port manifold, so the low end torque should be good.



I ordered a 3/8" hose connector for the rear port, so I could use that for the PCV. The chap from whom I bought the engine - it has 25,000 miles on it - had a pair rocker covers with takeoffs at the rear and a cross-hose and T fitting that vented into the back of his Holley. Doesn't mean it worked of course, I never asked him.
But is it a good idea to vent below the secondaries which most of the time are closed?

Or I suppose I could drill out the front plug then hope to find a piece of tube and epoxy it in there.

Or I could sell the 1404 and buy a new one with the tube, which seems a rather extreme solution.

I'm not very keen on venting into the air filter. That sends all the fumes through the carb and it seems to me that this carb needs to be clean if it's going to work well.

Just a little thing, but is illustrates why it can take so long to make a good V8 conversion.

Ivor

Edit: or I could go from the flame trap to a catch tank and from there into the filter. Like this, although the owner said it didn't work as the pipes were too small.
[www.flickr.com]



Edited 1 time(s). Last edit at 08/23/2017 05:20AM by 88v8.

Ivor, you've seen the amount of blowby at idle, now imagine what that's going to be under full load. THAT is the main issue you are dealing with, and if you think for an instant that you can suck it all through a 3/8" tube you are deluding yourself. As the engine gets older it just gets worse.

You've got basically 3 choices here. Vent to atmo, suck it down the carb throat, or find some way to introduce it to the intake behind the carb without completely screwing up your idle. Sounds like you are leaning towards the 3rd choice. The danger is too much on one end and too little on the other. I've plumbed mine through a 5/8" vacuum controlled heater valve and so far it works, but it's a unique solution. If you thoroughly investigate the methods used on modern engines you may find something that will work for you. I think most use electronic controls these days.

I dunno, maybe you can find a European car that used a 4bbl V8 and copy that system. That would probably be the easiest for you. But don't cut corners thinking you can overlook any element of the system, it'll bite you if you do. You need to fully understand how it works in all phases and it is a complex system. Much more complicated in operation than on this side because you actively involve the engine seals.

Now as for sending it through the carb, yeah it isn't optimal but it's been proven to work over decades of factory cars. The blowby has already combusted so it tends to richen the mixture as it goes through the carb and reduces the effective airflow as well. The oil and combustion byproducts it carries can dirty the carb but most is washed off by gasoline. American manufacturers used that system from the mid 60's up until EFI overtook it and not without good reasons. Even so, the functioning of the PCV valve itself is not commonly understood at all, and for such a simple device it's operating phases are complex. It needs to be carefully selected and then properly installed, best done by copying factory specs.

Jim

Ivor.
You can drill out the plug in the front port and tap it to 1/4" pipe thread (NPT)
Then you can put in any fitting that you wish.
No it's not ideal to vent the PCV to the rear of the carb but it works.
You will get the odd puff of smoke due to oil pooling from time to time.
That's why the front port is routed to mix the vapors with the incoming idle fuel mix.
GM did use the rear port for awhile but emissions rules dictated a change to the front 50 or so years ago.
Use the "ported" or timed vacuum port on the right hand side of the carb for your distributor.
The old "full manifold' vacuum method was used to aid the old weak starters by retarding the timing when cranking.
The timed port improves throttle response, reduces stalling and lessens emissions.
If I were doing it I would run the flame arrester hose to the air filter and drill out the filter on the left valve cover for a PCV valve. Run a hose to the front of the carb, and you're done. If possible reversing the valve covers would make a tidier installation. But I don't think that you have the room.

Cheers
Fred

Seriously Fred? Both the front and rear ports are exposed to full manifold vacuum and it makes zero difference to the intake mixture where the PVC fumes enter as it will be evenly distributed.
As for ported or timed vacuum for the distributor, that was a feeble attempt at emission control by retarding the timing at idle, therefore increasing engine and exhaust temperatures. If you want better throttle response, gas mileage and a cooler running engine, connect the vacuum advance to full manifold vacuum. I'd be happy to send you multiple links on the subject by professional engine builders as well as engineers.
I've been building and tuning performance engines for well over 40 years and every single one performed better with full vacuum over ported vacuum.

I am serious Jim.

I'm also a professional engine builder, tuner and an engineer.
I've received the highest possible awards from every manufacturer that I've ever worked for, been in magazines and I'm published.
Not trying to upset anyone and I won't pretend to know everything, but I will state what I do know.

Cheers
Fred

Well then you should know what you posted about ported vacuum is 100% wrong. Here's a quote from an article written by John Hinckley. If you don't know who he is, he was an engineer and plant manager for GM as well as Chrysler and instrumental in the design and development of the Viper. He's written 1000's of articles as well as being inducted into the Corvette Hall of Fame.
[www.corvettemuseum.org]
“Ported Vacuum” was strictly an
early pre-converter crude emissions strategy and nothing more. Don’t believe
anyone who tells you that ported vacuum is a good thing for performance and
drivability – it’s not. Anyone with a street-driven car without manifold-connected
vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and
fuel economy, probably because they don’t understand what vacuum advance is,
how it works, and what it’s for. There are lots of long-time experienced mechanics
who don’t understand the principles and operation of vacuum advance either, so
they’re not alone."



Edited 1 time(s). Last edit at 08/24/2017 12:00PM by MGBV8.

Wow Jim,
Didn't mean to get your Cheerios all soggy!
I know what works for me so I suggest that we respectfully agree to disagree.

Cheers
Fred

Quote:

No problem Fred. I just didn't want others to think what you posted was true. It may work for you but others that have resumès and accomplishments that makes yours, if it's actually real as you say (doubtful), look like an application to kindergarten.
Your post is equivalent to me saying "greasing your brake pads/shoes makes you stop quicker".

Interesting. When I was growing up and you wanted an expert opinion you went down to the corner shop to the guy that did it for a living every day. That was the way it worked back then. It's amazing how the Internet changed all that. Suddenly there are, it seems, millions of experts. To be one all you have to do is use Google. The wonders of the modern world. I'll stick with Fred with his real world experiences.



Edited 1 time(s). Last edit at 08/24/2017 11:59AM by MGBV8.

Easy there guys, no need to get upset. This is a debate that absolutely rages and it's best to just stay away from it and do what you want to do. I respect both of your opinions and your right to them, whether I agree or not, and I'll just say that Max and I have had these very same discussions and neither one of us is going to convince the other. We are still friends, even if he is wrong. ;-)

The problem is that despite a clear history, under the right conditions advantages can be found to ported vacuum. It usually occurs when the engine and more specifically the distributor was designed for port vacuum but that does not negate the advantage. So I now say, if your distributor was designed for ported vacuum (and you lack the ability and desire to do a complete re-curve) then use ported vacuum. If it was designed for manifold vacuum, then use that.

There's no reason we can't be civil.

Jim

I absolutely agree Jim B.
Everyone has their opinions and they deserve to be respected.
If I have offended anyone I humbly apologize.

Jim D.
Once confronted by your logic.
I find that I would be unable to defend myself.
And so we are done here.

Thanks
Fred

What happened to the old wisdom that performance engines do not need vacuum advance at all ???

Sorry I couldnt resist :-)

Like I said I ran the same carb with Performer intake. I had a Unilite dizzy with only mechanical advance. It really would have benefited from a vacuum advance as well. It´s easy to test, just advance the timing say 10 degrees and try ro run the car. Gently of course, timing will be too advanced at full load.

The thing is, the advance curve needed to be adjusted to make the engine happy. The same fact applies to the ported vs. timed advance. It´s all about the parts and the combination. Each engine is individual, I am sure that professional engine builders do agree. Especially when the engine is fitted to a car.

A good example: I have a Morris Mini with a turbo, intercooler and a single blowtru SU HIF44. It has a basic Lucas dizzy with vacuum advance ! And only advance, not advance at vacuum/retard at boost. The centrifugal advance curve is very conservative and it needs full time vacuum to run like it is intended. Disconnect the vacuum and it is an absolute slouch. Sure, another dizzy less vacuum might work but that´s how it was designed from the factory. Even a locked dizzy would work somehow.

I have seen comments that performance engines don't need vac advance.

I also see this site belonging to RPI Engineering, one of the leading Rover V8 specialists where he says to use the timed port.
[www.v8engines.com]
[scroll down about an inch]

In the Edelbrock installation manual it says to use the timed port for emissions controlled engines, and the manifold port for non-emissions.

The Lucas dizzie on my car is a 1982 model, set up to run off the SUs. It has the half-baked emissions system of that period, so I need to run it to suit. If I expose the dizzie to full vacuum, it will not give the correct curve. Ideally of course it would all be set up on the rolling road to suit the different advance profile of the Edelbrock, but at the moment I just need to have a rolling car with the minimum of complications :}

Now I could pretend that I have suddenly become all knowledgable on this subject, but actually I swiped this from elsewhere:

The vacuum advance modules that were originally fitted to the early Rover engines offered slight variations in their operationg points. Some would range from 4" Hg to 15"Hg, whilst others ranged from 4"Hg to 20"Hg. The actual degrees of advance provided was typically 8 degrees at the distributor thus 16 degrees at the crankshaft.

The vacuum advance modules available today [this was 2009] for the Rover V8 have been standardised, with one module being supplied as an OEM for all engines that had such modules fitted. These modules provide vacuum advance from 5"Hg to 17"Hg and will see 8 degrees at the distributor thus 16 degrees at the crankshaft of advance.

Vacuum advance as it applies to the Rover V8 with SU carburettors is a ported system, with the vacuum supply point being before the butterfly therefore no vacuum advance is provided at idle. When cruising with minimal throttle opening, vacuum is high so typically the module will be providing essentially its fully rated maximum advance,..ie 16 degrees, while at greater throttle openings ranging upto full throttle, vacuum will continue to diminish so the supplied advance will also decline until none is supplied..

So without getting into the merits of which could be superior in a performance engine on an optimised distributor, I think for my humble road car I had better stick with ported vacuum.

As regards the PCV, I take the point about trying to suck all the vapour through a 3/8" hole, so I'll try the simple method of running from the flame trap into the filter. If that doesn't work, I'll have to get more sophisticated.

I do note however, that the 1963 first gen 327 in my Rambler just has a little pcv valve in a 3/8" line to the carb adaptor, and no connection to the filter, but then, that's the way it was designed.

Onwards.

Ivor



Edited 1 time(s). Last edit at 08/24/2017 04:44AM by 88v8.

That was entertaining....